1. Field of the Invention
The present invention relates generally to surge suppressor circuits for electrical equipment and more particularly relates to a surge suppressor circuit having a thermally activated fail-safe shunting device.
2. Description of the Prior Art
Surge suppressor circuits for protecting sensitive electronic equipment are well known in the prior art. These circuits typically present a high impedance (open circuit) to circuit ground under normal signal conditions and present a low impedance (short circuit) to circuit ground when a voltage or a current exceeds a predetermined threshold. For momentary voltage or current surges, such as lightning and noise spikes, the surge suppressor components are only activated for a short duration. In this condition, there is little thermal heating of the surge suppressing device typically used in such circuits. However, in those cases where a signal line being protected contacts a constant voltage supply line whose voltage exceeds the threshold voltage of the surge suppressor circuit, the surge suppressor continually conducts to circuit ground. This results in severe heating of the device. Absent thermal protection, this constant heating condition can result in a fire or in the failure of the surge suppressor.
It is an object of the present invention to provide a surge protector for electrical communication lines which substantially reduces overheating conditions in the surge protector.
It is another object of the present invention to provide a surge protector for electrical communication lines which can handle momentary voltage or current surges on the lines as well as a constant excessive voltage or current.
It is a further object of the present invention to provide a coaxial surge protection device for transmission lines which minimizes the chance of damage to the surge protector and failure thereof due to an overheating condition which may otherwise have led to damage of the electrical equipment to which the transmission line is connected.
It is still another object of the present invention to provide a coaxial surge suppressor circuit which overcomes the inherent disadvantages of conventional surge suppressors.
In a preferred form, the present invention provides a coaxial surge suppressor circuit with a thermally activated fail-safe shunting circuit. In accordance with one form of the present invention, a surge protector for electrical signal communication or transmission lines, such as for the transmission of data or telephony signals, includes a transmission line having associated therewith a circuit ground, and a surge suppressor element electrically coupled between the transmission line and circuit ground. A thermally activated shunt assembly is thermally coupled to the surge suppressor element. The thermally activated shunt assembly senses an overheating condition with respect to the surge suppressor element and electrically shunts the surge suppressor element upon sensing the overheating condition.
These and other objects, features and advantages present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.